This invention relates to apparatus for the treatment of water supplies with a gas for sterilization, pH control etc.
Water supplies must normally be treated before they are safe or suitable for consumption. One major type of treatment involves the chlorination of water to sterilize it. In this process a supply of gaseous chlorine is brought into contact with the water supply in a special apparatus, normally referred to in the water treatment art as a chlorinator. The same, or similar apparatus can also be used for treatment of water with sulphur dioxide or ammonia. For pH control the same or similar apparatus can be used to treat the water with carbon dioxide.
Apparatus of this type is required to carry out a number of operations in the treatment process. The supply of gas will usually be from a high pressure source, for example pressurized cylinders of chlorine gas. The actual mixing of the gas with the water is carried out at sub-atmospheric pressure in a venturitype device, normally referred to as an ejector, in which the flow of water from a jet creates a low-pressure zone into which gas is introduced. It is therefore necessary for the high pressure source of gas to be converted into a low pressure supply. Thus apparatus of this type includes a control system normally referred to as a vacuum regulator in which the high pressure gas is allowed to expand with a corresponding pressure drop before being passed to the next part of the apparatus. The vacuum regulator is generally provided with venting means to allow a surge of pressure to be released by venting the gas to the atmosphere.
Conventionally, the vacuum regulator passes the gas to a monitoring system designed to provide a warning if the pressure is incorrect (either too high or too low). From here the gas passes to a flow measuring device, conventionally a floating cone flowmeter giving a visual indication of the rate of flow of gas.
The gas next passes to a control valve serving to control the output of gas to the ejector. This valve is conventionally a linear response valve of the type where the flow is directly proportional to the displacement of a control knob or wheel. This control valve may be manually operated or may be to a greater or lesser extent automated. The control valve is normally fitted with a vacuum override relief valve serving to allow the intake of atmospheric air if the pressure drops too far.
From the control valve the gas passes to the ejector where it is mixed with the water. An optional refinement in the system is the incorporation of a differential control valve which is responsive to changes in the pressure difference between the control valve and the ejector (for example caused by fluctuations in the water supply pressure). A differential control valve of this type generally includes a diaphragm valve which adjusts the pressure in the gas flow in response to changes in pressure in the ejector.
Apparatus of this type is well known and has been in use for very many years with considerable success. However, the main problem which is encountered in this type of apparatus results from the need to use corrosive gases such as chlorine and sulphur dioxide. All pipework interconnecting the various elements in the apparatus has to withstand the gas with each joint secure against leakage.